Increasing volumes of communications traffic are now being carried on packet networks, and in particular on Internet Protocol (IP) networks. Such networks comprise nodes or routers interconnected by links so as to define a mesh. A recent introduction has been the concept of a network having an optical core in which traffic is carried on switched optical fiber paths between routers. The core is accessed by an edge networks Typically in the design of high capacity IP networks. routers are classified as either core routers or edge routers. Edge routers carry out all the network ingress and egress functions, in particular controlling the incoming traffic streams across the network. Core routers act as transit routers forwarding network traffic from one network node to another.
In such a network, the user data is assembled into packets and each packet is provided with a header identifying the destination of the packet and optionally, including routing information. The header may further contain information misting to the router chosen to route the packet contents and identifying a priority class for the packet. For example, packets containing high quality of service real time traffic, such as voice, will be accorded the highest priority, while packets containing ‘best efforts’ data may be accorded a low priority.
A particular problem that has been experienced with certain types of traffic, particularly data traffic and real-time video traffic, is its inherently bursty nature. Further, this burstiness occurs on a timescale that is shorter than feasible network control loop timescales, and thus can lead to congestion when traffic is heavy. When congestion occurs, ordinary data traffic which is not critically time sensitive can be briefly buffered in the routers which are experiencing congestion. Urgent data traffic and real time interactive services such as voice and video cannot be delayed.
In order to maximize the overall network utilization, it is desirable to perform statistical multiplexing of traffic traversing the network while providing a prior allocation of resources and protection particularly for the delay sensitive traffic Existing control and feedback mechanisms are however inadequate to respond to this bursty traffic at a sufficiently rapid rate to provide this resource allocation and protection. In The conventional approach to this problem, the high speed statistical variations in traffic flow are simply allowed for by setting large margins in the setting of control levels for determining feedback price. Proposals for ‘pricing’ ingress flows at the edge of the network for admission control purposes have involved for instance measuring the ‘effective bandwidth’ of the flow. Effective bandwidth is a measure of the bandwidth that needs to be reserved to give a desired packet loss for delay rate on a statistically varying flow. Unfortunately, effective bandwidths do not add linearly on aggregation and so are difficult to use in a congestion price feedback control scheme.